1. Field of the Invention
The present invention relates to a filter cloth traveling type belt filter for use in the production of toner particles contained in a toner which is for developing an electrostatic charge latent image in an image forming method such as electrophotography, electrostatic recording method and toner jet method, and a production method of toner particles.
2. Description of the Related Art
Toner particles having a desired particle size are formed in a liquid dispersion medium to obtain a dispersion liquid of toner particles in suspension polymerization method and dissolution suspension method. Then, the toner particles are separated from the dispersion liquid of the toner particles with a separation unit typically represented by a solid-liquid separation apparatus such as a filter apparatus and washed to remove impurities. The cake of the obtained wet toner particles is dried, classified as needed, and then supplemented with predetermined additives to produce a toner (see Japanese Patent Application Laid-Open No. S51-014895).
In emulsion polymerization method, a monomer composition containing a polymerizable monomer, a polymerization initiator, a surfactant, and further containing a cross-linking agent, a chain transfer agent, and the other additives as needed are dispersed in an aqueous medium with a stirrer and subjected to polymerization reaction to obtain emulsified resin particles having a desired particle size. In the meantime, a coloring agent is uniformly microdispersed in an aqueous medium containing a surfactant and associated (aggregated and fused) with the emulsified resin particles to obtain a dispersion liquid of toner particles having a desired particle size.
Then, filtration, washing, drying, classification are performed as in suspension polymerization method and dissolution suspension method to produce a toner (see Japanese Patent Application Laid-Open No. H05-265252).
As for the toner particles granulated in such a wet process, there has been proposed a method including separating toner particles from the dispersion liquid of toner particles, for example, with a belt filter having a filter cloth and a vacuum tray closely contacted with each other, and then washing and drying the toner particles (see Japanese Patent Application Laid-Open No. 2002-365839). According to the method described in Japanese Patent Application Laid-Open No. 2002-365839, toner particles are efficiently separated and washed from the dispersion liquid of toner particles, and thereby a toner having excellent image characteristics can be obtained.
In late years, however, high-definition images comparable to photographs in image quality are required of electrophotographic images due to diversified needs of users. One of the effective approaches to obtain high-definition images in electrophotography is to make small sized toner particles. When this small sizing of particles is performed by crushing, large energy is necessary, which is not preferable. On the other hand, it is easy to make the particles small sized in the wet granulation method. When this small sizing of particles is performed, however, dehydration ability deteriorates at the time of separation of toner particles from the dispersion liquid of the toner particles even when the belt filter mentioned above is used, and the water content of the obtained wet toner particle cake tends to increase. It is assumed that this is resulted from increase in the surface area of the particles per unit volume of a cake formed of wet toner particles. The deterioration in the dehydration ability increases the load in the drying step, which is a post process, and gives thermal damage to the toner particles. Thus, deterioration in image characteristics such as occurrence of photographic fog is resulted.
Accordingly, a solid-liquid separation apparatus as described in Japanese Patent No. 3311417 has been suggested as an apparatus for reducing the water content of the cake.
This apparatus is an apparatus which performs solid-liquid separation and drying by pressurizing a wet toner particle cake formed on a belt filter with a perforated plate and further pressurizing the cake by passing gas through the perforations.
However, the above-mentioned apparatus, when applied to a production method of a toner, only presses a plate on a wet toner particle cake, and therefore, there has been such a problem that the wet toner particles are blown out of the press surface where the wet toner particle cake and the plate are closely contacted when the gas is ejected through the perforations.
In addition, since the ejected gas leaks out of the press surface, it becomes difficult to allow the gas to sufficiently pass through the wet toner particle cake. As a result, there has been such a problem that an increase in the water content remaining in the cake and unevenness of the water content in the cake are caused.
As a solid-liquid separation apparatus which solves these problems, a solid-liquid separation apparatus as described in Japanese Patent Application Laid-Open No. 2006-297366 has been suggested. It is described that this apparatus presses a frame-like or annular sealing member 22 as described in FIGS. 15 and 16 on a tray and a wet toner particle cake 1 supplied on the surface of the tray, thereby preventing the cake from being scattered when a pressurized and aerated filtering is performed and enabling a stable filtering. Here, FIG. 15 is a schematic view of the apparatus which views the pressurization/aeration part from the cake traveling direction, and FIG. 16 is a drawing which views the pressurization/aeration part from below.
When this method is applied as a toner production method, the water content of wet toner particle cake 1 can be reduced, but dehydration is not sufficient in order to meet the high quality requirement of images demanded in late years. Therefore, a production apparatus and a production method which further improve dehydration ability are demanded. In addition, the frame-like or annular sealing member, particularly the sealing member which presses a slope surface of the filtration part, is subjected to shear stress and significantly degraded. Consequently, when continuous operation is performed, the sealing condition of the gas for aeration deteriorates and the dehydration ability deteriorates. Therefore, a decrease in the area of the sealing member which presses the slope surface of the filtration part has been eagerly expected.
In addition, there has been proposed in Japanese Patent Application Laid-Open No. 2007-058201 a production process including performing dehydration by compressed aeration after subjecting a toner particle dispersion liquid to solid-liquid separation. This process enables more dehydrated toner particle cake to be obtained with the use of the most suitable sealing member and operation conditions when dehydration is performed by means of compressed aeration. However, dehydration ability was not yet sufficient for meeting the high quality requirement of images demanded in late years and besides the degradation of a sealing member has not been sufficiently suppressed.
An object of the present invention is to provide a production apparatus and a production method of toner particles which have solved the problems as mentioned above. That is, an object of the present invention is to provide a production apparatus and a production method of toner particles which efficiently reduce the water content of a wet toner particle cake obtained by separating toner particles from a toner particle dispersion liquid and washing the toner particles in a production apparatus and a production method of toner particles granulated in a wet process.
Another object of the present invention is to provide a filter cloth traveling type belt filter for use in the production of toner particles overcoming the problems in the production process which a wet toner particle cake having a high water content brings about and having excellent image characteristics and to provide a production method of the toner particles.